Let's say I am meditating for 2-3 hours each day. How long would it take?
How long would it take to enter?
That's like asking how long would it take for you to start tasting the curries that are already on your plate. Or like asking how long will it take for you to taste almonds and cashews when you are eating a mix of nuts. It's just a matter of you deciding to practice awareness on them.
When your mind wanders thinking about past/present/future or when your mind becomes concentrated/scattered, you can be mindful of it to practice the 3rd Satipattana
If you decide to practice mindfulness on seeing, hearing, smelling, tasting etc. or the five hindrances, that's the 4th Satipattana.
The cultivating of Satipatthāna consists of kāyānupassanā, vēdanānupassanā, cittānupassanā, and dhammānupassanā, is a systematic, guaranteed way, of attaining Nibbāna, by purification of the being, i.e., via cleansing one’s mind. In it Buddha says:
“Katame cattāro? Idha, bhikkhave, bhikkhu kāye kāyānupassi viharati ātāpī sampajānō, satimā vineyya lōke abhijjhā dōmanassam. Vedanāsu vedanānupassi viharati ātāpī sampajānō, satimā vineyya lōke abhijjhā dōmanassam. Citte cittänupassī viharati ātāpī sampajānō, satimā vineyya lōke abhijjhā dōmanassam. Dhammesu dhammānupassi viharati ātāpī sampajānō, satimā vineyya lōke abhijjhā dōmanassam”
“ātāpi” is to remove that “fire” from the heart and the stress from the mind, and calm the mind. This is the “cooling down”, the early stages of Nibbāna. In the Buddha’s last words: “..”appamadēna sampādēta” or “..make haste and sort out “immoral tendencies”. When one has done “sampādēta” one becomes “sampajannō”: One knows what is right and what is wrong automatically; it has become a habit. “sati ma vineyya lōke abhijjhā dōmanassam” means establishing moral mindset and moral conduct in order to be free from the debt-ridden world and to be relieved from abhijja and domanassa. This is the key to “cooling down”
Thus we should strive to “get rid of the fire or heat in the mind by being aware of kilesa or defilements and by removing extreme greed (abhijja) that leads to a depressed mind (domanassa)”. This “cooling down” is done in four ways: kāyānupassanā, vēdanānupassanā, cittānupassanā, and dhammānupassanā..
These are somewhat sequential, in the sense that one needs to start with taking care of major sources of abhijjā and domanassa with kāyānupassanā. One needs to be aware that one’s actions and speech need to be moral, i.e., to abstain from dasa akusala as much as possible. With the mind clear of the worst hindrances, then it will be easier to learn Dhamma with dhammānupassanā, be easier not to react to feelings (vēdanānupassanā) but to take time and evaluate consequences, and to automatically be aware of immoral thoughts that come to the mind (cittānupassanā). Thus, it is gradual process. Each advance helps with gaining confidence in one’s actions, helps not to just react to feelings, helps to think with a clear head, which in turn helps with the understanding process.